Manufacture of flexible films



y 1966 c. H. PHILLIPS ETAL 3,

MANUFACTURE OF FLEXIBLE FILMS Filed Feb. 16, 1962 an, M Ml e/ /97 7dRUE?S United States Patent 3,249,216 MANUFACTURE OF FLEXIBLE FILMS Cyril Howard Phillips, Durleigh, Bridgwater, and Cedric Michael Lnlham and Brian Lyall, Bridgwater, England, assignors to British Cellophane Limited, Bridgwater,

England, a British company 'Filed Feb. 16, 1962, Ser. No. 173,821

12 Claims. (Cl. 206-59) This invention relates to the'manufacture of flexible films such as cellulose film and films of plastic materials, such as, for example, polyethylene, which are commonly used for wrapping and packaging purposes.

In the manufacture of such flexible films, it is common practice to wind the product into roll or reel form for convenience of storage and transport. The films as manufactured usually have lanes of varying thickness in the longitudinal direction and on winding into a roll, the thicker portions are superimposed upon each other at each turn and build up intohard circumferential bands. As tension is applied to the film on winding to ensure that the windings are sufficiently tight to avoid telescoping of the roll, the layers of film wound over the hard bands are distorted. This distortion is accentuated during storage of the roll when the film shrinks due to the release of the stretch which occurred during winding under tension, and so tightens the windings. On unwinding the film from such rolls, it is found that the distortion due to being wound over the hard bands is permanent and difiiculties arise in converting such film into bags or in printing on a printing machine where it is necessary for the film to lie fiat in order to avoid creases and defective printing;

The object of the present invention is to provide a method for producing rolls of film having substantially no hard circumferential bands.

Accordingly, the present invention includes a process for the treatment of a film having variations in thickness across the width whereby it can be wound into a roll substantially free from hard circumferential bands which process comprises applying a solid particulate material uniformly to at least one side of the film in a total amount with the range between 0.001 S and 0.025 S grams per square metre of film, where S is the specific gravity of the particulate material and where the average particle size of the particulate material is within the range between and 45 microns.

On winding the film into a roll, the solid particles which have been uniformly deposited on the film lie between the individual windings and, it is believed, space the indi vidual windings apart.

At the positions where thick portions of the film lie in superimposition the particles are either crushed or forced partly into the surfaces of the adjacent film portions during winding and subsequent shrinkage whereas at the thinner portions the particles are substantially unafiected so that the roll is substantially free from hard bands and the layers of the film wound on the roll are not distorted. It is preferred, for convenience, to apply the particulate material to one surface of the film only. However, if the material is applied to both surfaces, when the film is wound into a roll, the material applied to one surface of the film will combine with the material applied to the other surface of the film in the space between the windmgs.

The process in accordance with the present invention is particularly useful when applied to cellulose film, which maybe either plain cellulose film or a cellulose film coated on one or both surfaces with a suitable heat-sealable and/or moisturep'roof coating composition. Examples of such coating compositions are nitrocellulose/ wax compositions, or polymeric products such as polyethylene or copolymers of vinylidene chloride which have been applied to the base cellulose film from a solution in a volatile solvent by a melt extrusion process or from aqueous dispersions.

The process in accordance with the invention may also :be applied to films manfactured from polymeric materials such as polyethylene, polypropylene, polyvinyl chloride, polyvinyl acetate, polyamides, or vinylidene chloride copolymers, either plain or coated with a suitable coating composition, or to laminates of like or dissimilar films.

When the film is coated with a coating composition which is applied from a solution in a volatile solvent or from an aqueous dispersion, it is preferable to apply the particulate material to the coated surface while the coating composition is still wet. Then, on drying the coated surface, the particles are held in position by the dry coating. Such coatings are normally about 1.2 microns in thickness.

In the case where the coating composition is a poly- Iner-ic material which is applied to the film in a molten state or the film is of a polymeric material and is formed by melt extrusion, the particulate material may conveniently be applied to the polymeric material surface before it solidifies on cooling. The particles become partly embedded in the surface of. the polymeric material such I that when the polymeric material solidifies, the particles are held in position on the surface.

A preferred solid particulate material for application to film in accordance with the invention is starch, particularly in view of its non-toxicity when the film is to be used for wrapping and packaging foodstuffs.

From bulk density measurements, it is found that starch particles have an average specific gravity of 1.0 and that for a sample of starch having an average particle size of 15 microns, there are about 6.O 10 particles per gram. It will be readily understood that for any particulate material having the same average particle size, there will be the same number of particles in separate samples of the materials when each sample is of a weight equal to the specific gravity of the material expressed in grams.

Other solid particulate materials which can be employed in the exercise of the invention are starch esters, resin coated starch particles, diatomaceous earths, silica, talc, or powdered polymers such as polyvinyl chloride or copolymers such as vinylidene chloride/acrylonitrile or vinylidene chloride/methyl methacrylate copolymer.

If the particulate material is applied to one surface or, in total, to both surfaces of the film in an amount less than 0.001XS grams per square metre (where S is the specific gravity of the particulate material), or the average particle size is less than 5 microns, then it is found that the benefits of the invention are not obtained, that is, the film on being wound into a. roll tends to develop hard circumferential bands. If, on the other hand, the particles applied to the film exceed 0.025 S grams per square metre, or the average particle size exceeds about 45 microns, then undesirable surface effects become apparent which render the film unattractive in appearance and deleteriously affect its printability. Further, Where the film is heat-scalable, excess particulate material tends to reduce the strength of the heat-seal bond, requiring the bonding temperature to be raised to undesirable values in order to obtain a satisfactory bond. Still further, excess particulate material tends to be rubbed off film converting machinery and accumulates on the working parts. I

In a preferred form of the invention and, in particular, when the film is to be printed in light tones by the gravure printing method, the total amount of particulate Average particle size micronsbetween 0.005 S and 0.020 S grams.

Average particle size micronsbetween 0.003 S and 0.015 S grams. Average particle size 45 micronsbetween 0.002 S and 0.0l0 S grams.

The invention also includes a roll of film when treated in accordance with the invention.

The invention is illustrated by the accompanying drawings in which:

FIGURE 1 is a side elevation of a powder applying apparatus, and

FIGURE 2 is a magnified portion of a section through 2 2 of a treated roll of film shown in FIGURE 1.

In FIGURE 1, a film 1 is passed over a guide roller 2 and vwound into a roll 3. Just prior to the film 1 reach ing the roll 3 it is sprayed on the upper surface with a solid particulate material 4 through a spraying nozzle 5. The solid particulate material 4 has a particle size of between 5 and 45 microns and is delivered at a measured rate to provide between 0.0018 and 0.0258 grams of material per square meter of film 1, where S is the specific gravity of the material 4.

In FIGURE 2, separate convolutions 6 of the film 1 are shown spaced apart by particles of the solid particulate material 4.

Specific methods of carrying the invention into effect will now be described by way of the following examples:

Example 1 A regenerated cellulose film which had been coated on both sides with a vinylidene chloride/ methyl methacrylate copolymer coating composition and dried was drawn at a tension of 1 pound per inch width and at a speed of 180 feet per minute past a powder dispenser such as is described in British patent application No. 13,366/ 61 and was wound into a roll. The coated film had an average thickness of 0.001 inch but varied in thickness across its width by 10.00008 inch due to the presence of longitudinal lanes of varying thickness formed during the manufacture of the coated film.

Starch powder having an average particle size of 15 microns and in which all the particles were substantially within the range between 10 and microns was applied uniformly to one side of the film from the dispenser at such a rate that the amount of starch applied per square metre of film surface was 0.008 gram. The starch particles had an average specific gravity of 1.0 when meas- 1v ured by bulk density methods.

The roll of film obtained had a smooth cylindrical appearance .and was free from hard circumferential bands. The roll was stored for three months. after storage the roll retained its smooth cylindrical appearance. On unwinding the film from the roll it was found to be capable of lying flat in the transverse crosssection and could be handled by printing and bag-making machinery without difiiculty.

By way of control, the procedure described above was repeated except that no starch was applied to the film. The roll of film obtained had a seriesof hard circumferential bands which became accentuated after storage and caused the surface of the roll to be distorted. On unwinding the film from the roll it was found that the film was distorted transversely and could not readily be held fiat when handled by converting machinery, resulting in It was noted that the formation of creases. The density of the roll obtained by weighing and measuring was found to be greater than the density of the roll of film treated with the starch particles.

Example 2 A regenerated cellulose film having, an average thickness of 0.0008 inch but a variation in thickness across its width of $000008 inch due to longitudinal lanes of varying thicknesses was coated on one side with an aqueous dispersion of a vinylidene chloride/methyl methacrylate copolymer. The wet surface was drawn at a speed of feet per minute past a powder dispenser such as is'described .in British patent application No. 13,366/61 charged with starch ester. powder having an average particle size of-l5 microns, the size ofthe particles being in the range of between 10 and '20 microns.

From bulk density measurements it was found that the specific gravity of the starch ester particles was 1.20.

The starchester powder was uniformly distributed on to the wet surface of the film at such a rate that the amount of powder applied per square metre of film surface was 0.010 gram per square metre.

The coating on the film was then dried by the application of radiant heat and the coated film was wound into a roll. The coating was-l.5 microns in thickness.

- The roll of film had a smooth cylindrical appearance and was free of hard circumfcrentialbands even after storage for two months. On unwinding the film from the roll, it was found that the film lay fiat in the transverse direction and scould be handled by converting machinery without difficulty.

The procedure was repeated with the exception that the application of powder was omitted. The roll of film was found to have hard cylindrical bands which became accentuated on storage and film unwound from the roll was distorted in the transverse direction and would not readily lie flat.

We claim:

1. A roll of film having variations in thickness across its width, said roll having a solid particulate material uniformly distributedin the space between the turns of the roll in an amount within the range between 0.001 XS and 0.025 S grams per square metre, where S is the specific gravity of the particulate material and where the average particle size of the particulate material is within the range between 5 and 45 microns, whereby said roll is substantially free from hard circumferential bands.

2. A roll of film as claimed in claim 1 in which the solid particulate material is uniformly distributed in the space between the turns in an amount within the range between 0.002 S and 0.020 S grams per square metre, where S is the specific gravity of the particulate material.

3. A roll of film as claimed in claim 1 inwhieh the solid particulate material is" fixed to one of the adjacent surfaces of-the film defining the space between the turns.

4. A roll of film as claimed in claim 1 in which the solid particulate material is, selected from the group of particulate materials consisting of a starch ester, diatomaceous earth, silica, tale, a powdered polymer and a powdered copolymer.

5. A roll of film as claimed in claiml in which the film is selected from the group of films consisting of cellulose, polyethylene, polypropylene, polyvinyl chloride, polyvinyl acetate, a polyamide and a vinylidene chloride copolymer.

6. A roll of film as claimed in claim 1, in which the solid particulate material is resin coated starch.

7. A roll of film as claimed in claim 1 in which the solid particulate material is starch.-

8. A roll of film as claimed in claim 7 in which the starch is distributed in the space between the turns of the roll in an amount within the range between 0.003 and 0.015 gram per square meter of film and the average particle size of the starch is 15 microns.

9. A process for the treatment of a film having variations in thickness across the width whereby it can be wound into a. roll substantially free from hard circumferential bands which process comprises coating the film with a coating composition, uniformly applying to at least one coated side of the film before the coating is set a solid particulate material in a total amount within the range between 0.001 XS and 0.025 S grams per square meter of film, where S is the specific gravity of the particulate material and the average particle size of the particulate material is within the range between 5 and 45 microns, and setting the coating.

10. A process as calimed in claim 9 in which the coating composition is applied to the film as a liquid and is dried by heat after the particulate material has been applied.

11. A process as claimed in claim 9 in which the coating composition is a polymeric material which is applied to the film in molten state and is set by cooling after the particulate material has been applied.

12. A process for the treatment of a film of a polymeric material formed by a melt extrusion method having variations in thickness across the width whereby it can be wound into a roll substantially free from hard circumferential bands which process comprises uniformly applying to at least one side of the film while it is in a molten 6 state, a solid particulate material in a total amount within the range between 0.001 S and 0.025 XS grams per square meter of film, where S is the specific gravity of the particulate material and the average particle size of the particulate material is within the range between 5 and microns and setting the film.

References Cited by the Examiner UNITED STATES PATENTS 2,074,313 3/1937 Abrams et a1.

2,303,826 12/ 1942 DeBell.

2,469,957 5/1949 Penn 167-92 X 2,558,776 7/1951 Olson et a1 206-59 2,653,885 9/1953 Harper 206-59 2,672,978 3/ 1954 Hickox 206-59 2,772,774 12/ 6 Rabuse 206-59 2,907,671 10/ 1959 Duvivier 117-16 3,964,174 12/ 1960 Litchfield et a1. 206-59 3,964,419 12/1960 Link et al 117-16 THERON E. CONDON, Primary Examiner.

EARLE J. DRUMMOND, GEORGE O. RALSTON,

Examiners.

I. M. CASKIE, Assistant Examiner. 

1. A ROLL OF FILM HAVING VARIATIONS IN THICKNESS ACROSS ITS WIDTH, SAID ROLL HAVING A SOLID PARTICULATE MATERIAL UNIFORMLY DISTRIBUTED IN THE SPACE BETWEEN THE TURNS OF THE ROLL IN AN AMOUNT WITHIN THE RANGE BETWEEN 0.001XS AND 0.025XS GRAMS PER SQUARE METRE, WHERE S IS THE SPECIFIC GRAVITY OF THE PARTICULATE MATERIAL AND WHERE THE AVERAGE PARTICLE SIZE OF THE PARTICULATE MATERIAL IS WITHIN THE RANGE BETWEEN 5 AND 45 MICRONS, WHEREBY SAID ROLL IS SUBSTANTIALLY FREE FROM HARD CIRCUMFERENTIAL BANDS. 